Re: sub-select with aggregate

Uz.ytkownik Stephan Szabo napisa?:
> But you can't do that anyway, because you don't expose group_id
> in the original query.  I assume user_id was a mistake then and was
> meant to be group_id or that both were meant to be in the
> select list.
Yes, I meant group_id, but in orginal query I didn't have to add 
group_id to select list.

> In the first case changing the order means that the output
> group_id column is X.group_id rather than users.group_id
> (using removes one of them which is why group_id isn't
> ambiguous.  In the second it uses on to get both group_ids
> and exposes the one from X.
The problem isn't ambigous columns, but speed.
I think Postgres first performs sub-query with all records from table 
(it takes very long time). After this Postgres permforms joining table 
with sub-query. The question is: How to speed up query like this? How to 
give param group_id from first table (users) to subquery?
Tomasz Myrta